There are two advantages for using the fractal structure in the conventional fractal antenna in the tradition. The first advantage is the characteristic of the self-similarity, a structure repeatability which has a plurality of similar replicated sub-structure, the scale of each of which sub-structure is gradually reduced, so that the same structural details in each smaller repeated sub-structure is replicated, resulting in easily producing multiple frequency effect for the application of the antenna. The second advantage is the space-filling characteristic in which the antenna can extend the current path in the limited space by the geometry of the fractal sub-structure within the limited space, resulting in achieving the lower resonant frequency band easily, and reducing the area occupied by the antenna to achieve the purpose of miniaturization.
However, using the fractal structure as the design of the antenna has several defects: (1) In order to retain the complete geometry of the fractal structure, the antenna will occupy a relatively larger area in the application of the mobile communication device; (2) For having the lowest resonant frequency band for the antenna, the load metal strip will be configured at the end of the fractal geometry structure. Although the current resonant path can be increased to achieve the low frequency effect, the load metal strip will destroy the kindness of minimizing the fractal structure antenna; (3) Using the microstrip line as the signal feed form: the signal feed of the fractal antenna and the connected ground plane thereof is non-coplanar, which renders the fractal antenna being difficult to integrate with the surface acoustic wave component, the high frequency component or the passive component of the mobile communication devices; and (4) As stated in (3), the microstrip line is usually used in the fractal antenna, and can easily lead to radiation losses, resulting in reducing the radiation efficiency, which is a major problem for applying in the low frequency band fractal antenna.
To sum up the above disadvantages, it is necessary to provide a new antenna structure for overcoming the above-mentioned defects. It is therefore attempted by the applicant to deal with the above situation encountered in the prior art.